In general, in a communication system in which a base station and a user terminal directly communicate with each other, when the user terminal is located in an area having a bad signal quality, such as a cell boundary area or a shaded area, it is difficult for the communication system to provide a reliable communication service.
In order to solve this problem, more attentions are recently being paid to a relay network which can extend the coverage and increase the system capacity with a relatively low cost. Especially, a relay node installed in a cell boundary area or a shaded area, which has a bad signal quality, can improve the system performance with a relatively low cost.
Usually, a relay network refers to a network in which a relay node relays a signal between a source node transmitting the signal and a destination node receiving the signal for expansion of the service coverage, increase of the system capacity, and so on.
For example, a signal transmitted by the source node is received by the destination node and the relay node. Further, the relay node transmits the signal received from the source node to the destination node. By receiving both the signal transmitted from the source node and the signal transmitted from the relay node, the destination node can increase the probability of successful reception.
The most representative technology of the relay network includes a relay-based network which is used in Wireless Personal Area Network (WPAN) based on the IEEE 802.15.3 standard.
For the relay network as described above, there is an urgent necessity to prepare a communication protocol, which not only can improve the performance of the network and reduce the number of times of channel uses, but can also achieve a stable performance in an actual wireless communication environment that is unable to guarantee the reliability.
Further, in order to improve the communication quality in a wireless communication environment having a rapid change in the channel characteristics, it is urgently required to prepare a scheme for rapidly allocating or changing an optimum communication link according to a change in the channel environment.